[Haskell-cafe] Simplest way to move a ... `using` ... line into the IO monad?

David Banas capn.freako at gmail.com
Fri Oct 27 19:04:36 UTC 2023

Thank you all for the quick replies!
`mapConcurrently` was exactly what I needed. :)

> On Oct 27, 2023, at 11:51 AM, Viktor Dukhovni <ietf-dane at dukhovni.org> wrote:
> On Fri, Oct 27, 2023 at 07:43:07PM +0100, Tom Ellis wrote:
>> On Fri, Oct 27, 2023 at 11:36:53AM -0700, David Banas wrote:
>>> What is the simplest way to translate a non-monadic line of Haskell code, such as:
>>> res = map foo xs `using` parList rseq
>>> For use in the IO monad?
>>> This doesn’t work:
>>> res <- mapM fooM xs `using` parTraversable rseq
>> The docs for Control.Parallel.Strategies say "The parallel tasks
>> evaluated by a Strategy may have no side effects. For
>> non-deterministic parallel programming, see Control.Concurrent."[1].
>> So I guess you should look into Control.Concurrent[2].
> For a more friendly interface:
>    https://hackage.haskell.org/package/async-2.2.4/docs/Control-Concurrent-Async.html <https://hackage.haskell.org/package/async-2.2.4/docs/Control-Concurrent-Async.html>
> If the number of concurrent tasks is reasonably modest, a good fit could
> be `mapConcurrently`.
> For much larger numbers of tasks, it is best to run the jobs at a
> bounded concurrency, which may bring a BoundedChan to which the items to
> process are written, another to which results are written and a set of
> threads that do the processing, repeatedly reading more data until the
> channel is drained. 
> *The* book on subject is: https://simonmar.github.io/pages/pcph.html <https://simonmar.github.io/pages/pcph.html>
> --
>    Viktor.
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